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%I #7 Jul 19 2018 08:23:13
%S 24,40,68,122,220,410,764,1454,2764,5330,10268,19982,38860,76130,
%T 149084,293534,577804,1141970,2256668,4472942,8865100,17610050,
%U 34979804,69601214,138485644,275900210,549658268,1096111502,2185812940,4362027170
%N Number of -2..2 arrays x(i) of n+1 elements i=1..n+1 with set{t,u,v in 0,1}((x[i+t]+x[j+u]+x[k+v])*(-1)^(t+u+v)) having two or four distinct values for every i,j,k<=n.
%H R. H. Hardin, <a href="/A211567/b211567.txt">Table of n, a(n) for n = 1..73</a>
%F Empirical: a(n) = 3*a(n-1) + 3*a(n-2) - 15*a(n-3) + 4*a(n-4) + 18*a(n-5) - 12*a(n-6).
%F Empirical g.f.: 2*x*(12 - 16*x - 62*x^2 + 79*x^3 + 77*x^4 - 94*x^5) / ((1 - x)*(1 - 2*x)*(1 - 2*x^2)*(1 - 3*x^2)). - _Colin Barker_, Jul 19 2018
%e Some solutions for n=5:
%e ..2...-2...-1....2...-2....1....0....0....0....0....1....1...-2....2....0...-1
%e ..1...-2....1....2....1...-1...-2...-1....1....1....0....2...-1....0....2...-1
%e ..0....2....1...-2...-2....1....0...-2....2....0....1....1....0...-2....0...-1
%e ..1....2...-1...-2....1....1...-2...-1....1...-1....0....2...-1....0...-2....1
%e ..2....2...-1...-2...-2....1....0....0....0....0...-1....1....0....2....0....1
%e ..1...-2...-1...-2....1....1...-2...-1....1...-1...-2....2...-1....0....2....1
%K nonn
%O 1,1
%A _R. H. Hardin_, Apr 16 2012